1. Field of the Invention
The present general inventive concept relates to an image forming apparatus utilizing an electrophotographic process, and more particularly, to a developing unit capable of evenly spreading pressure of a developer and preventing the developer from being scattered, and an image forming apparatus having the developing unit.
2. Description of the Related Art
Image forming apparatuses utilizing electrophotographic processes perform operations such as charging, exposing, developing, transferring and fixing in order to form images. Developing units within the image forming apparatus function to develop electrostatic latent images formed on photosensitive media using a developer. Developing units include developer housings containing developer, and developing rollers. The developer contained in the developer housings is attached to developing rollers, and a developing gap of a predetermined distance is formed between the developing rollers and photosensitive media. Electrostatic forces generated by a potential difference between the developing rollers and photosensitive media cause the developer attached to developing rollers to move to photosensitive media through the developing gap, so that visual images corresponding to the electrostatic latent images are formed.
There are two types of developing units, one of which is manufactured with developer pre-supplied to developer housings, and the other one of which does not have the developer pre-supplied.
In the case of a developing unit in which developer is not pre-supplied to developer housings, it is impossible to check whether the developing unit is of inferior quality after the developing unit has been manufactured, since there is no developer in the developing unit with which to perform a print test.
In the case of a developing unit in which developer is pre-supplied, it is possible to sort out defective products by performing a print test. However, problems may arise during distribution before the developing units reach customers.
Developer as powders have an adhesive quality, and thus if a developing unit is placed in an upright position for a long period of time or is transported a long distance, the developer particles may become coagulated on one side of the developing unit. Accordingly, the pressure of the developer particles may increase, and the torque required to transfer the developer particles may increase excessively due to the coagulated developer particles. Therefore, the load on a motor may become excessive, causing the motor to be unable to rotate, and making it impossible for printing to be performed.
A developing roller rotates while a developing unit is being operated, causing airflow to be generated in a developing gap between the developing roller and a photosensitive medium, and accordingly, some developer scatters outwards from the developing unit in the direction of the airflow rather than moving onto the photosensitive medium. Additionally, a portion of the airflow formed in the developing gap flows into a developer housing, so the air pressure inside the developer housing becomes greater than the air pressure outside the developer housing. Such a difference in air pressure may cause a greater amount of developer to be scattered, and an image forming apparatus and printing media may thus be contaminated due to the scattered developer.
In order to prevent the scattering of developer, it is necessary for the air pressure in the developer housing to be reduced. To achieve this, there is provided a conventional developer housing including a filter and an air vent hole formed therein. The filter only allows air to pass through while preventing the developer from passing through. However, fine developer particles having a diameter less than that of pores formed on the filter are able to flow out through the air vent hole. If a developing unit is attached to an image forming apparatus, there is a small possibility that fine developer particles flow out. However, since shocks or vibrations may be applied to the developing unit during distribution before the developing units reach customers, the outflow of fine developer particles may increase.